Metabolism of
Branched-Chain Amino Acids in Starved Rats: The
Role of Hepatic Tissue M. HOLEČEK,
L. ŠPRONGL1, I. TILŠER2
Department of Physiology, Faculty of
Medicine, Charles University, Hradec Králové, 1University
Hospital Motol, Prague, 2Department
of Pharmacology, School of Pharmacy, Hradec
Králové, Czech Republic
Received February 15,
2000
Accepted May 16, 2000
Summary
Parameters
of branched-chain amino acids (BCAA; leucine,
isoleucine and valine) and protein metabolism
were evaluated using L-[1-14C]leucine
and a-keto[1-14C]isocaproate (KIC) in
the whole body and in isolated perfused liver
(IPL) of rats fed ad libitum or starved for 3
days. Starvation caused a significant increase in
plasma BCAA levels and a decrease in leucine
appearance from proteolysis, leucine
incorporation into body proteins, leucine
oxidation, leucine-oxidized fraction, and leucine
clearance. Protein synthesis decreased
significantly in skeletal muscle and the liver.
There were no significant differences in leucine
and KIC oxidation by IPL. In starved animals, a
significant increase in net release of BCAA and
tyrosine by IPL was observed, while the effect on
other amino acids was non-significant. We
conclude that the protein-sparing phase of
uncomplicated starvation is associated with
decreased whole-body proteolysis, protein
synthesis, branched-chain amino acid (BCAA)
oxidation, and BCAA clearance. The increase in
plasma BCAA levels in starved animals results in
part from decreased BCAA catabolism, particularly
in heart and skeletal muscles, and from a net
release of BCAA by the hepatic tissue.
Key
words
Nutrition
· Starvation · Leucine · Protein Metabolism ·
Branched-chain amino acids
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Dr. Milan Holeček, Department of Physiology,
Charles University, Faculty of Medicine, Šimkova
870, 500 01 Hradec Králové, Czech Republic, fax
+420-49-5210190, e-mail: holecek@lfhk.cuni.cz
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